The invention relates to a lithium cell, a battery comprising the lithium cell, and motor vehicle, mobile device, or stationary storage element comprising said battery.
Lithium cells are used with ever-increasing frequency in numerous applications as energy storage means particularly because of their high energy density/specific energy and their long service life and low self-discharge losses. For example lithium cells are already employed as batteries in motor vehicles, in particular as energy storage means in electric cars, in particular as accumulators in mobile electronic devices and in stationary storage means.
As used herein, the term “lithium cells” is understood to mean for example rechargeable lithium accumulators (secondary cells) or primary non-rechargeable lithium cells. In particular, lithium cells also comprise lithium ion accumulators, which comprise anodes and cathodes that can intercalate and deintercalate lithium ions, and lithium accumulators, which comprise anodes comprising metallic lithium.
Lithium cells comprise an electrolyte which is arranged within/between two different electrodes, the anode and the cathode, energy being stored electrochemically by transformation of chemical energy into electrical energy. The medium between the two electrodes must fulfill at least two functions. One function is that of accommodating the electrolyte while simultaneously ensuring lithium ion conduction within the electrode and between the anode (negative electrode) and cathode (positive electrode), The further function is that of insulating the two electrodes from one another electrically and mechanically to prevent electrical shorts.
Polymer membranes, for example based on polyethylene (PE), are often employed as so-called separators which are both permeable to the ions of the electrolyte solution and also insulate electrodes from one another electrically and mechanically. While these separators are cheap they exhibit only low thermal and mechanical stability, said separators being deformed above 90° C. and melting/areal shrinking of the polymer membrane already sating in above 130° C. In particular these polymer membranes can also be penetrated by lithium dendrites, for example, which can grow on the anode side during operation of the lithium cells. Furthermore, on account of their low polarity the polyethylene membranes can undergo only poor wetting by the polar, nonaqueous electrolyte solutions of the lithium cells.
DE 36 03 196 A1 discloses a process for producing a lead accumulator comprising a gel electrolyte. In contrast to lithium cells, in lead accumulators, energy is stored through chemical transformations of the electrodes and of the electrolyte. To produce this gel electrolyte a certain amount of fiber material, for example polyethylene or polypropylene is admixed, together with the accumulator acid, sulfuric acid, to a sol-gel batch made of silicic acid and introduced into the cell of the lead accumulator. After gelation, an electrolyte gel is formed that is reinforced by the fibers present therein. The disadvantage of this system is that in principle it cannot be employed for lithium cells inter alia because of the acidic, aqueous electrolyte. Furthermore, silicic acid is also not suitable as a gelating agent for lithium cells since silicic acid does not undergo physical and chemical interaction with liquid electrolytes. Silicic acid is highly hygroscopic and difficult to dry and would introduce moisture/water into a lithium cell which negatively affects service life and performance.
The invention is based on the object of providing a lithium cell that is improved with regard to the above mentioned disadvantages. The invention provides a lithium cell, for example a lithium ion accumulator. The invention also provides batteries comprising the lithium cells and motor vehicles or mobile devices/stationary storage means comprising the batteries.